A Study on the Strengthening of Rc Beams using Textile Reinforcement

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A STUDY ON THE STRENGTHENING OF RC BEAMS USING TEXTILE

REINFORCEMENT

P.B Jayakrishnan

1

_{,Paul Shaji}

2

1_{PG Student, Dept. of Civil Engineering, Mar Athanasius College of Engineering, Kerala, India}

2Assistant Professor, Dept. of Civil Engineering, Mar Athanasius College of Engineering, Kerala, India

---*---Abstract -**

Textile reinforcement concrete is a new

technology of composite material which can even replace reinforcement to some extent . Textile reinforcement is a common method for retrofitting of concrete structures . These textile reinforcement comprises fabric meshes . Jute , glass fibres , Nylons etc are the most commonly used fabric meshes . This project is mainly concerned on the strengthening of concrete structures by providing textile reinforcement. The beam sections used in this research is of size 150 x 250 mm and of 1500mm in length. The beam is designed for 5 ton. When 50KN is applied to the beam, it will fail. After failure the beam is repaired using retrofitting method with basalt textile mesh. Some beams are retrofitted before applying load and a comparison in strength of beam before and after using basalt mesh is studied.. Flexural strength was determined and crack pattern studies were carried out .The effectiveness of various profiles of wrappind is studied and maximum deflection and maximum load comparison is made.

Key Words: (Textile reinforced concrete, Fibre reinforced mortar, Textiles, Compressive Strength, Flexural Strength, Textile reinforced mortar

1.INTRODUCTION

Textile reinforcement is now being a common method for retrofitting of concrete structures. Textiles comprise fabric meshes made of long woven, knitted or even unwoven fibre rovings in at least two (typically orthogonal) directions. Mortarsin which the textile reinforcement is embedded serve as binders containing polymeric additives inorder to have improved strength properties. Materials with high tensile strengths with negligible elongation properties are reinforced with woven or unwoven fabrics. The fibres used for making the fabric are of high tenacitylike Jute, Glass, Fibre, Kevlar, Polypropylene, Polyamides (Nylon) etc.

1.1 Need for textile reinforcement

The use of fibre reinforced polymers (FRP) in strengthening and retrofitting projects has gained increasing popularity among structural engineers, due to numerous attractive features of these materials, such as: high specific strength (i.e. strength to weight ratio), corrosion resistance, ease and speed of application and minimal change of cross sections. Despite its advantages over other methods, the FRP

strengthening technique is not entirely problem-free. The organic resins used as to bind and impregnate the fibres entail a number of drawbacks, namely: (a) poor behaviour at temperatures above the glass transition temperature; (b) relatively high cost of resins; (c) potential hazards for the manual worker;One possible course of action aiming at the solution of the drawbacks of FRP would be the replacement of organic binders with inorganic ones, e.g. cement based mortars, leading to the substitution of FRP with fibre reinforced mortars (FRM). The problem arising from such a substitution would be the relatively poor bond conditions in the resulting cementitious composite as, due to the granularity of the mortar. Fibre matrix interactions could be enhanced when continuous fibre sheets are replaced by TEXTILES. The latter comprise fabric meshes made of long woven, knitted or even unwoven fibre rovings in at least two (typically orthogonal) directions. The quantity and the spacing of rovings in each direction can be controlled independently, thus affecting the mechanical characteristics of the textile and the degree of penetration of the mortar matrix through the mesh openings. It is through this mechanical interlock that an effective composite action of the mortar-grid structure is achieved. For the cementitious matrix, the following requirements should be met: non-shrinkable; high workability; high viscosity; low rate of workability loss (application of each mortar layer should be possible while the previous one is still in a fresh state); and sufficient shear (hence tensile) strength, in order to avoid premature debonding.

1.2

Textile reinforced concrete

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higher strengths for TRC than in FRC.

2.

TEXTILE MATERIALS

Textile fibres have a great influence on the strength of composite materials, their properties as well as their magnitude. Materials which are most applicable for use in TRC structures are alkali-resistant glass (AR-glass), carbon

and aramid fibres. Besides these materials, basalt, steel and polymer fibres such as PBO can also be used. Steel fibre yarns are however not economically feasible. Comparisons between them are shown below in Table 1.

Table -1

Textile Diameter range Density Tensile strength Young’s modulus Advantages Disadvantages (m) (kN/m3)_(GPa) _(GPa)

AR–

glass 9 to 27 2800 1.4 70 to 80

Very good adhesion to concrete

Low tensile strength

Carbon 7 1800 2 to 5 200 to 450 Superior tensile _strength Expensive

Aramid 12 1400 3 60 to 130 Low density low _brittleness

Negative heat expansion, low resistance to alkali attacks

Basalt 9 to 13 2600 2.99 95 High elongation and equivalent

thickness Expensive

PBO 8 2445 5.80 270 High strength Expensive

From the above table, it is clear that these fibres have great strengthening capacity. Their high tensile strength and their good resistance to corrosion, for example, make them a good choice for a reinforcing material. Despite the fact that they remain expensive and present some challenges in regards to production, these fibres nevertheless are reasonable alternatives to traditional steel bars or short fibres.

2.2

Concrete matrix

The concrete used for TRC needs to fulfil demands, mechanical properties and durability, which are necessary to get proper composite material behaviour. Usually the maximum grain size used is less than 2mm, thus the concrete matrix is also called fine-grained concrete. Matrix composition should have chemical compatibility with textile reinforced materials, consistency for full penetration, planned production process and mechanical properties for load-carrying capacity of a TRC element

2.3 Basalt fabric meshes

Basalt textile meshes is used here for retrofitting of RC beams. Basalt mesh Geo grid is available in different sizes with epoxy coatings for concrete and composites and asphalt coatings for asphalt reinforcement.

Basalt mesh is better than steel for many reasons

 Stronger than steel wire of comparable size

 Far lighter and easier to handle and install

 Will not rust or corrode or cause cracking of concrete

 Flexible for easier design

 Does not conduct electricity or induce electric field

 It binds well with asphalt and concrete

Basalt fiber geo grid mesh is used for reinforcing asphalt concrete(covering in construction, reconstruction and repair of airport, runways, highways and any pavements, pedestrain ways, road inclines and banks).

The reinforcement with basalt mesh increases the overall reliability, safety and the cutting process output. The strength of basalt mesh is as good metal reinforcement, however it is 2.6 times lighter, thereby simplifying transportation and handling in construction. It is more durable than metallic and glass fiber reinforcement due to its excellent performance.

3 BEAM CASTING

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in to the mould .a cover of 25mm is provided and a cover block is used for it, . Pour the concrete in to the mould and compact the specimen by needle vibrator.

Fig 1: Longitudinal section of the beam

Fig 2: Beam reinforced with steel rebar 3.1 Testing of beams

[image:3.595.40.276.140.207.2]

The specimens casted were tested for their failure load using loading frame of capacity 5 ton after 28 daysThe apparatus used for testing the specimen is a loading frame of capacity 10 tonnes.the loading frame consisted of steel frames to transfer the load to foundation and pumps and jack to apply the load to specimen. There was only one type of jack available in the labouratory and it was of capactity 10 ton.

Fig 3 : Loading aarangement of the specimen

3.2 Failure load

[image:3.595.41.275.234.418.2]

The specimen casted were tested for their failure load .the specimens were placed on the loading frame with two end simply supported. The load was applied manualy at a constant rate without shock. For testing of beams, hydraulic jack of 10Ton capacity was used and a plate section was placed below the jack and 2 rollers were placed below the plate sections for uniformly transfering the load throughout the beam. The beams were placed above the I section with roller support at distance 75mm from both ends, beam was placed over the roller support, spacing between the rollers is 1000mm.load is applied corresponding deflections are measured till the beam fails. load applied was measured using a dial gauge with 0.01T accuracy.

Fig 4: Crack pattern after loading 3.3 Retrofitting of RC beams

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temperature before testing.

Fig 5: Fixing the basalt mesh over the beam using epox resin

4. Test results

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We have tested the beams and noted the various loads and their corresponding deflections. 7.4 KN ia the ultimate load of the control specimen. After retrofitting this control specimen with basalt textile mesh using epoxy resin , the ultimate load was found to be 9.4KN. Also comparison has been made on their strength and deformations.

Table 1:Load and corresponding deflection values of control specimen before and after retrofitting

Fig 6: Strength comparison of beams using graph

Fig 7: Strength comparison of control specimen

Fig 8:Deflection comparison of control specimen

5. CONCLUSION

Based on experimental investigations the flexural behaviour of reinforced concrete beams externally strengthened by basalt fibre is studied.From the test results and calculated strength values the following conclusions are drawn

1. The strengthened beams showed a remarkable increase in the flexural toughness.

2. Ductile failure was noticeable in comparison with the brittle failure of unstrengthened beam.

3. Retrofitting of control specimen using basalt textile mesh is effective as the flexural strength of the control specimen is increased by 30-35%.

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A Study on the Strengthening of Rc Beams using Textile Reinforcement